Coding interpolation filter type

ABSTRACT

Decoding a video stream may include decoding a first block of a current frame by decoding a first motion vector from the encoded video stream, decoding an identifier of a first interpolation filter from the encoded video stream, and reconstructing the first block using the first motion vector and the first interpolation filter. Decoding a second block of the current frame may include identifying the first motion vector from the first block as a selected motion vector for predicting the second block in response to decoding an inter-prediction mode identifier for decoding the second block, identifying the first interpolation filter as a selected interpolation filter for predicting the second block in response to identifying the first motion vector from the first block as the selected motion vector for predicting the second block, and reconstructing the second block using the first motion vector and the first interpolation filter.

BACKGROUND

Digital video can be used, for example, for remote business meetings viavideo conferencing, high definition video entertainment, videoadvertisements, or sharing of user-generated videos. Due to the largeamount of data involved in video data, high performance compression isneeded for transmission and storage. Various approaches have beenproposed to reduce the amount of data in video streams, includingcompression and other encoding and decoding techniques. These techniquesmay involve subpixel interpolation for fractional motion.

SUMMARY

This application relates to encoding and decoding of video stream datafor transmission or storage. Disclosed herein are aspects of systems,methods, and apparatuses related to associating a motion vector with aninterpolation filter type for inter-predicted blocks of a video dataframe.

An aspect is a method for video decoding using an interpolation filtertype associated with a decoded motion vector. The decoding may includedecoding a first block of a current frame from an encoded video stream,decoding, by a processor in response to instructions stored on anon-transitory computer readable medium, a second block of the currentframe from the encoded video stream, and outputting or storing the firstblock and the second block. Decoding the first block may includedecoding a first motion vector from the encoded video stream, decodingan identifier of a first interpolation filter from the encoded videostream, and reconstructing the first block using the first motion vectorand the first interpolation filter. Decoding the second block mayinclude identifying the first motion vector from the first block as aselected motion vector for predicting the second block in response todecoding an inter-prediction mode identifier for decoding the secondblock, identifying the first interpolation filter as a selectedinterpolation filter for predicting the second block in response toidentifying the first motion vector from the first block as the selectedmotion vector for predicting the second block, and reconstructing thesecond block using the first motion vector and the first interpolationfilter.

Another aspect is a method for video decoding using an interpolationfilter type associated with a decoded motion vector. The decoding mayinclude decoding, by a processor in response to instructions stored on anon-transitory computer readable medium, a current block of a currentframe from an encoded video stream, and outputting or storing thecurrent block. Decoding the current block may include identifyingpreviously decoded blocks spatially proximal to the current block in thecurrent frame, identifying a motion vector from a selected previouslydecoded block from the previously decoded blocks spatially proximal tothe current block as a selected motion vector for predicting the currentblock, identifying an interpolation filter in response to identifyingthe motion vector as a selected interpolation filter for predicting thecurrent block, and reconstructing the current block using the selectedmotion vector and the selected interpolation filter.

Another aspect is a method for video encoding using an interpolationfilter type associated with a motion vector. The encoding may includegenerating a first encoded block by encoding a first block from acurrent frame from an input video stream, outputting the first encodedblock, generating, by a processor in response to instructions stored ona non-transitory computer readable medium, a second encoded block byencoding a second block from the current frame, and transmitting orstoring the output bitstream. Encoding the first block may includeidentifying a first motion vector for predicting the first block, andidentifying a first interpolation filter for predicting the first block.Outputting the first encoded block may include including the firstmotion vector in an output bitstream, and including an identifier of thefirst interpolation filter in the output bitstream. Encoding the secondblock may include identifying candidate motion vectors for predictingthe second block. The candidate motion vectors may include the firstmotion vector, and a second motion vector for predicting the secondblock, wherein the second motion vector differs from the first motionvector, and wherein the second motion vector is a non-zero motionvector. Encoding the second block may include identifying, from thecandidate motion vectors, a selected motion vector for predicting thesecond block, and on a condition that the selected motion vector is thefirst motion vector, identifying the first interpolation filter as aselected interpolation filter for predicting the second block, andomitting the selected motion vector for predicting the second block andan identifier of the selected interpolation filter for predicting thesecond block from the output bitstream.

Variations in these and other aspects will be described in additionaldetail hereafter.

BRIEF DESCRIPTION OF THE DRAWINGS

The description herein makes reference to the accompanying drawingswherein like reference numerals refer to like parts throughout theseveral views.

FIG. 1 is a diagram of a computing device in accordance withimplementations of this disclosure.

FIG. 2 is a diagram of a computing and communications system inaccordance with implementations of this disclosure.

FIG. 3 is a diagram of a video stream for use in encoding and decodingin accordance with implementations of this disclosure.

FIG. 4 is a block diagram of an encoder in accordance withimplementations of this disclosure.

FIG. 5 is a block diagram of a decoder in accordance withimplementations of this disclosure.

FIG. 6 is a block diagram of a motion vector having subpixel accuracy inaccordance with implementations of this disclosure.

FIG. 7 is a flowchart diagram of a process for encoding using aninterpolation filter associated with an encoded motion vector inaccordance with implementations of this disclosure.

FIG. 8 is a flowchart diagram of a process for decoding using aninterpolation filter associated with a decoded motion vector inaccordance with implementations of this disclosure.

DETAILED DESCRIPTION

Video compression schemes may include breaking each image, or frame,into smaller portions, such as blocks, and generating an outputbitstream using techniques to limit the information included for eachblock in the output. An encoded bitstream can be decoded to re-createthe source images from the limited information. In some implementations,the information included for each block in the output may be limited byreducing spatial redundancy, reducing temporal redundancy, or acombination thereof. For example, temporal or spatial redundancies maybe reduced by predicting a frame based on information available to boththe encoder and decoder, and including information representing adifference, or residual, between the predicted frame and the originalframe.

In some implementations, motion prediction may include using aninter-prediction mode in which portions of a reference frame arecompared with a block in a current frame. A motion vector may be definedto represent a block or pixel offset between the reference frame and thecorresponding block or pixels of the current frame. However, indicatingthe motion vector in the output bitstream may increase the size of theoutput bitstream, which may reduce encoding efficiency. In someimplementations, encoding efficiency may be improved by encoding blocksusing motion vectors previously used for encoding neighboring, orspatially proximal, blocks. For example, the encoder may evaluateneighboring previously encoded blocks to identify candidate motionvectors for encoding the current block, may select one of the candidatemotion vectors from the neighboring previously encoded blocks as themotion vector for coding the current block, may indicate aninter-prediction mode corresponding to the selected motion vector in theoutput bitstream, and may omit indicating the motion vector forpredicting the current block in the output bitsream.

In some implementations, an interpolation filter may be used to adjustfor sub-block or sub-pixel motion between the reference frame and thecurrent frame. Subpixel motion may also be referred to as subpel motionor fractional pixel motion. In some embodiments, the encoder mayidentify a motion vector and a subpixel interpolation filter forencoding a block and may indicate the motion vector and an identifier ofthe subpixel interpolation filter in the encoded video stream. Forexample, the encoder may evaluate neighboring previously encoded blocksto identify candidate motion vectors for encoding the current block, mayselect one of the candidate motion vectors from the neighboringpreviously encoded blocks as the motion vector for coding the currentblock, may indicate an inter-prediction mode corresponding to theselected motion vector in the output bitstream, may omit indicating themotion vector for predicting the current block in the output bitsream,and may indicate an identifier of the subpixel interpolation filter forpredicting the current block in the output bitstream. However,indicating the identifier of the subpixel interpolation filter in theoutput bitstream may increase the size of the output bitstream, whichmay reduce encoding efficiency.

In some embodiments, encoding efficiency may be improved by encodingblocks using interpolation filters previously used for encodingneighboring, or spatially proximal, blocks. For example, the encoder mayevaluate neighboring previously encoded blocks to identify candidatemotion vectors for encoding the current block, may select one of thecandidate motion vectors from the neighboring previously encoded blocksas the motion vector for coding the current block, may identify theinterpolation filter used for encoding the neighboring previouslyencoded block corresponding to the selected motion vector, may indicatean inter-prediction mode corresponding to the selected motion vector andthe identified interpolation filter in the output bitstream, and mayomit indicating the motion vector and the identified interpolationfilter for predicting the current block in the output bitstream.

FIG. 1 is a diagram of a computing device 100 in accordance withimplementations of this disclosure. A computing device 100 can include acommunication interface 110, a communication unit 120, a user interface(UI) 130, a processor 140, a memory 150, instructions 160, a powersource 170, or any combination thereof. As used herein, the term“computing device” includes any unit, or combination of units, capableof performing any method, or any portion or portions thereof, disclosedherein.

The computing device 100 may be a stationary computing device, such as apersonal computer (PC), a server, a workstation, a minicomputer, or amainframe computer; or a mobile computing device, such as a mobiletelephone, a personal digital assistant (PDA), a laptop, or a tablet PC.Although shown as a single unit, any one or more element of thecomputing device 100 can be integrated into any number of separatephysical units. For example, the UI 130 and the processor 140 can beintegrated in a first physical unit and the memory 150 can be integratedin a second physical unit.

The communication interface 110 can be a wireless antenna, as shown, awired communication port, such as an Ethernet port, an infrared port, aserial port, or any other wired or wireless unit capable of interfacingwith a wired or wireless electronic communication medium 180.

The communication unit 120 can be configured to transmit or receivesignals via a wired or wireless medium 180. For example, as shown, thecommunication unit 120 is operatively connected to an antenna configuredto communicate via wireless signals. Although not explicitly shown inFIG. 1 , the communication unit 120 can be configured to transmit,receive, or both via any wired or wireless communication medium, such asradio frequency (RF), ultra violet (UV), visible light, fiber optic,wire line, or a combination thereof. Although FIG. 1 shows a singlecommunication unit 120 and a single communication interface 110, anynumber of communication units and any number of communication interfacescan be used.

The UI 130 includes any unit capable of interfacing with a user, such asa virtual or physical keypad, a touchpad, a display, a touch display, aspeaker, a microphone, a video camera, a sensor, or any combinationthereof. The UI 130 can be operatively coupled with the processor, asshown, or with any other element of the computing device 100, such asthe power source 170. Although shown as a single unit, the UI 130 mayinclude one or more physical units. For example, the UI 130 may includean audio interface for performing audio communication with a user, and atouch display for performing visual and touch based communication withthe user. Although shown as separate units, the communication interface110, the communication unit 120, and the UI 130, or portions thereof,may be configured as a combined unit. For example, the communicationinterface 110, the communication unit 120, and the UI 130 may beimplemented as a communications port capable of interfacing with anexternal touchscreen device.

The processor 140 can include any device or system capable ofmanipulating or processing a signal or other information now-existing orhereafter developed, including optical processors, quantum processors,molecular processors, or a combination thereof. For example, theprocessor 140 can include a special purpose processor, a digital signalprocessor (DSP), a plurality of microprocessors, one or moremicroprocessor in association with a DSP core, a controller, amicrocontroller, an Application Specific Integrated Circuit (ASIC), aField Programmable Gate Array (FPGA), a programmable logic array,programmable logic controller, microcode, firmware, any type ofintegrated circuit (IC), a state machine, or any combination thereof. Asused herein, the term “processor” includes a single processor ormultiple processors. The processor is operatively coupled with thecommunication interface 110, the communication unit 120, the UI 130, thememory 150, the instructions 160, and the power source 170 in theexample of FIG. 1 .

The memory 150 can include any non-transitory computer-usable orcomputer-readable medium, such as any tangible device that can, forexample, contain, store, communicate, or transport the instructions 160,or any information associated therewith, for use by or in connectionwith the processor 140. The non-transitory computer-usable orcomputer-readable medium can be, for example, a solid state drive, amemory card, removable media, a read only memory (ROM), a random accessmemory (RAM), any type of disk including a hard disk, a floppy disk, anoptical disk, a magnetic or optical card, an application specificintegrated circuits (ASICs), or any type of non-transitory mediasuitable for storing electronic information, or any combination thereof.The memory 150 can be connected to, for example, the processor 140through, for example, a memory bus (not explicitly shown).

The instructions 160 can include directions for performing any method,or any portion or portions thereof, disclosed herein. The instructions160 can be realized in hardware, software, or any combination thereof.For example, the instructions 160 may be implemented as informationstored in the memory 150, such as a computer program, that may beexecuted by the processor 140 to perform any of the respective methods,algorithms, aspects, or combinations thereof, as described herein. Theinstructions 160, or a portion thereof, may be implemented as a specialpurpose processor, or circuitry, that can include specialized hardwarefor carrying out any of the methods, algorithms, aspects, orcombinations thereof, as described herein. Portions of the instructions160 can be distributed across multiple processors on the same machine ordifferent machines or across a network such as a local area network, awide area network, the Internet, or a combination thereof.

The power source 170 can be any suitable device for powering thecommunication interface 110. For example, the power source 170 caninclude a wired power source; one or more dry cell batteries, such asnickel-cadmium (NiCd), nickel-zinc (NiZn), nickel metal hydride (NiMH),lithiumion (Li-ion); solar cells; fuel cells; or any other devicecapable of powering the communication interface 110. The communicationinterface 110, the communication unit 120, the UI 130, the processor140, the instructions 160, and the memory 150 are operatively coupledwith the power source 170.

Although shown as separate elements, the communication interface 110,the communication unit 120, the UI 130, the processor 140, theinstructions 160, the power source 170, the memory 150, or anycombination thereof can be integrated in one or more electronic units,circuits, or chips.

FIG. 2 is a diagram of a computing and communications system 200 inaccordance with implementations of this disclosure. The computing andcommunications system 200 may include one or more computing andcommunication devices 100A/100B/100C, one or more access points210A/210B, one or more networks 220, or a combination thereof. Forexample, the computing and communication system 200 can be a multipleaccess system that provides communication, such as voice, data, video,messaging, broadcast, or a combination thereof, to one or more wired orwireless communicating devices, such as the computing and communicationdevices 100A/100B/100C. Although, for simplicity, FIG. 2 shows threecomputing and communication devices 100A/100B/100C, two access points210A/210B, and one network 220, any number of computing andcommunication devices, access points, and networks can be used.

A computing and communication device 100A/100B/100C can be, for example,a computing device, such as the computing device 100 shown in FIG. 1 .As shown, the computing and communication devices 100A/100B may be userdevices, such as a mobile computing device, a laptop, a thin client, ora smartphone, and the computing and communication device 100C may be aserver, such as a mainframe or a cluster. Although the computing andcommunication devices 100A/100B are described as user devices, and thecomputing and communication device 100C is described as a server, anycomputing and communication device may perform some or all of thefunctions of a server, some or all of the functions of a user device, orsome or all of the functions of a server and a user device.

Each computing and communication device 100A/100B/100C can be configuredto perform wired or wireless communication. For example, a computing andcommunication device 100A/100B/100C can be configured to transmit orreceive wired or wireless communication signals and can include a userequipment (UE), a mobile station, a fixed or mobile subscriber unit, acellular telephone, a personal computer, a tablet computer, a server,consumer electronics, or any similar device. Although each computing andcommunication device 100A/100B/100C is shown as a single unit, acomputing and communication device can include any number ofinterconnected elements.

Each access point 210A/210B can be any type of device configured tocommunicate with a computing and communication device 100A/100B/100C, anetwork 220, or both via wired or wireless communication links180A/180B/180C. For example, an access point 210A/210B can include abase station, a base transceiver station (BTS), a Node-B, an enhancedNode-B (eNode-B), a Home Node-B (HNode-B), a wireless router, a wiredrouter, a hub, a relay, a switch, or any similar wired or wirelessdevice. Although each access point 210A/210B is shown as a single unit,an access point can include any number of interconnected elements.

The network 220 can be any type of network configured to provideservices, such as voice, data, applications, voice over internetprotocol (VoIP), or any other communications protocol or combination ofcommunications protocols, over a wired or wireless communication link.For example, the network 220 can be a local area network (LAN), widearea network (WAN), virtual private network (VPN), a mobile or cellulartelephone network, the Internet, or any other means of electroniccommunication. The network can use a communication protocol, such as thetransmission control protocol (TCP), the user datagram protocol (UDP),the internet protocol (IP), the real-time transport protocol (RTP) theHyper Text Transport Protocol (HTTP), or a combination thereof.

The computing and communication devices 100A/100B/100C can communicatewith each other via the network 220 using one or more a wired orwireless communication links, or via a combination of wired and wirelesscommunication links. For example, as shown the computing andcommunication devices 100A/100B can communicate via wirelesscommunication links 180A/180B, and computing and communication device100C can communicate via a wired communication link 180C. Any of thecomputing and communication devices 100A/100B/100C may communicate usingany wired or wireless communication link, or links. For example, a firstcomputing and communication device 100A can communicate via a firstaccess point 210A using a first type of communication link, a secondcomputing and communication device 100B can communicate via a secondaccess point 210B using a second type of communication link, and a thirdcomputing and communication device 100C can communicate via a thirdaccess point (not shown) using a third type of communication link.Similarly, the access points 210A/210B can communicate with the network220 via one or more types of wired or wireless communication links230A/230B. Although FIG. 2 shows the computing and communication devices100A/100B/100C in communication via the network 220, the computing andcommunication devices 100A/100B/100C can communicate with each other viaany number of communication links, such as a direct wired or wirelesscommunication link.

Other implementations of the computing and communications system 200 arepossible. For example, in an implementation the network 220 can be anad-hock network and can omit one or more of the access points 210A/210B.The computing and communications system 200 may include devices, units,or elements not shown in FIG. 2 . For example, the computing andcommunications system 200 may include many more communicating devices,networks, and access points.

FIG. 3 is a diagram of a video stream 300 for use in encoding anddecoding in accordance with implementations of this disclosure. A videostream 300, such as a video stream captured by a video camera or a videostream generated by a computing device, may include a video sequence310. The video sequence 310 may include a sequence of adjacent frames320. Although three adjacent frames 320 are shown, the video sequence310 can include any number of adjacent frames 320. Each frame 330 fromthe adjacent frames 320 may represent a single image from the videostream. A frame 330 may include blocks 340. Although not shown in FIG. 3, a block can include pixels. For example, a block can include a 16×16group of pixels, an 8×8 group of pixels, an 8×16 group of pixels, or anyother group of pixels. Unless otherwise indicated herein, the term‘block’ can include a superblock, a macroblock, a segment, a slice, orany other portion of a frame. A frame, a block, a pixel, or acombination thereof can include display information, such as luminanceinformation, chrominance information, or any other information that canbe used to store, modify, communicate, or display the video stream or aportion thereof.

FIG. 4 is a block diagram of an encoder 400 in accordance withimplementations of this disclosure. Encoder 400 can be implemented in adevice, such as the computing device 100 shown in FIG. 1 or thecomputing and communication devices 100A/100B/100C shown in FIG. 2 , as,for example, a computer software program stored in a data storage unit,such as the memory 150 shown in FIG. 1 . The computer software programcan include machine instructions that may be executed by a processor,such as the processor 140 shown in FIG. 1 , and may cause the device toencode video data as described herein. The encoder 400 can beimplemented as specialized hardware included, for example, in computingdevice 100.

The encoder 400 can encode an input video stream 402, such as the videostream 300 shown in FIG. 3 to generate an encoded (compressed) bitstream404. In some implementations, the encoder 400 may include a forward pathfor generating the compressed bitstream 404. The forward path mayinclude an intra/inter-prediction unit 410, a transform unit 420, aquantization unit 430, an entropy encoding unit 440, or any combinationthereof. In some implementations, the encoder 400 may include areconstruction path (indicated by the broken connection lines) toreconstruct a frame for encoding of further blocks. The reconstructionpath may include a dequantization unit 450, an inverse transform unit460, a reconstruction unit 470, a loop filtering unit 480, or anycombination thereof. Other structural variations of the encoder 400 canbe used to encode the video stream 402.

For encoding the video stream 402, each frame within the video stream402 can be processed in units of blocks. Thus, a current block may beidentified from the blocks in a frame, and the current block may beencoded.

At the intra/inter-prediction unit 410, the current block can be encodedusing either intra-frame prediction, which may be within a single frame,or inter-frame prediction, which may be from frame to frame.Intra-prediction may include generating a prediction block from samplesin the current frame that have been previously encoded andreconstructed. Inter-prediction may include generating a predictionblock from samples in one or more previously constructed referenceframes. Generating a prediction block for a current block in a currentframe may include performing motion estimation to generate a motionvector indicating an appropriate reference block in the reference frame.

The intra/inter-prediction unit 410 may subtract the prediction blockfrom the current block (raw block) to produce a residual block. Thetransform unit 420 may perform a block-based transform, which mayinclude transforming the residual block into transform coefficients in,for example, the frequency domain. Examples of block-based transformsinclude the Karhunen-Loève Transform (KLT), the Discrete CosineTransform (DCT), and the Singular Value Decomposition Transform (SVD).In an example, the DCT includes transforming a block into the frequencydomain. The DCT includes using transform coefficient values based onspatial frequency, with the lowest frequency (i.e., DC) coefficient atthe top-left of the matrix and the highest frequency coefficient at thebottom-right of the matrix.

The quantization unit 430 may convert the transform coefficients intodiscrete quantum values, which may be referred to as quantized transformcoefficients. The quantized transform coefficients can be entropyencoded by the entropy encoding unit 440 to produce entropy-encodedcoefficients. Entropy encoding can include using a probabilitydistribution metric. The entropy-encoded coefficients and informationused to decode the block, which may include the type of prediction used,motion vectors, and quantizer values, can be output to the compressedbitstream 404. The compressed bitstream 404 can be formatted usingvarious techniques, such as run-length encoding (RLE) and zero-runcoding.

The reconstruction path can be used to maintain reference framesynchronization between the encoder 400 and a corresponding decoder,such as the decoder 500 shown in FIG. 5 . The reconstruction path may besimilar to the decoding process discussed below, and may includedequantizing the quantized transform coefficients at the dequantizationunit 450 and inverse transforming the dequantized transform coefficientsat the inverse transform unit 460 to produce a derivative residualblock. The reconstruction unit 470 may add the prediction blockgenerated by the intra/inter-prediction unit 410 to the derivativeresidual block to create a reconstructed block. The loop filtering unit480 can be applied to the reconstructed block to reduce distortion, suchas blocking artifacts.

Other variations of the encoder 400 can be used to encode the compressedbitstream 404. For example, a non-transform based encoder can quantizethe residual block directly without the transform unit 420. In someimplementations, the quantization unit 430 and the dequantization unit450 may be combined into a single unit.

FIG. 5 is a block diagram of a decoder 500 in accordance withimplementations of this disclosure. The decoder 500 can be implementedin a device, such as the computing device 100 shown in FIG. 1 or thecomputing and communication devices 100A/100B/100C shown in FIG. 2 , as,for example, a computer software program stored in a data storage unit,such as the memory 150 shown in FIG. 1 . The computer software programcan include machine instructions that may be executed by a processor,such as the processor 160 shown in FIG. 1 , and may cause the device todecode video data as described herein. The decoder 400 can beimplemented as specialized hardware included, for example, in computingdevice 100.

The decoder 500 may receive a compressed bitstream 502, such as thecompressed bitstream 404 shown in FIG. 4 , and may decode the compressedbitstream 502 to generate an output video stream 504. The decoder 500may include an entropy decoding unit 510, a dequantization unit 520, aninverse transform unit 530, an intra/inter-prediction unit 540, areconstruction unit 550, a loop filtering unit 560, a deblockingfiltering unit 570, or any combination thereof. Other structuralvariations of the decoder 500 can be used to decode the compressedbitstream 502.

The entropy decoding unit 510 may decode data elements within thecompressed bitstream 502 using, for example, Context Adaptive BinaryArithmetic Decoding, to produce a set of quantized transformcoefficients. The dequantization unit 520 can dequantize the quantizedtransform coefficients, and the inverse transform unit 530 can inversetransform the dequantized transform coefficients to produce a derivativeresidual block, which may correspond with the derivative residual blockgenerated by the inverse transform unit 460 shown in FIG. 4 . Usingheader information decoded from the compressed bitstream 502, theintra/inter-prediction unit 540 may generate a prediction blockcorresponding to the prediction block created in the encoder 400. At thereconstruction unit 550, the prediction block can be added to thederivative residual block to create a reconstructed block. The loopfiltering unit 560 can be applied to the reconstructed block to reduceblocking artifacts. The deblocking filtering unit 570 can be applied tothe reconstructed block to reduce blocking distortion, and the resultmay be output as the output video stream 504.

Other variations of the decoder 500 can be used to decode the compressedbitstream 502. For example, the decoder 500 can produce the output videostream 504 without the deblocking filtering unit 570.

In some implementations, reducing temporal redundancy may include usingsimilarities between frames to encode a frame using a relatively smallamount of data based on one or more reference frames, which may bepreviously encoded, decoded, and reconstructed frames of the videostream. For example, a block or pixel of a current frame may be similarto a spatially corresponding block or pixel of a reference frame. Insome implementations, a block or pixel of a current frame may be similarto block or pixel of a reference frame at a different portion, andreducing temporal redundancy may include generating motion informationindicating the spatial difference, or translation, between the locationof the block or pixel in the current frame and corresponding location ofthe block or pixel in the reference frame.

In some implementations, reducing temporal redundancy may includeidentifying a block or pixel in a reference frame, or a portion of thereference frame, that corresponds with a current block or pixel of acurrent frame. For example, a reference frame, or a portion of areference frame, which may be stored in memory, may be searched for thebest block or pixel to use for encoding a current block or pixel of thecurrent frame. For example, the search may identify the block of thereference frame for which the difference in pixel values between thereference block and the current block is minimized, and may be referredto as motion searching. In some implementations, the portion of thereference frame searched may be limited. For example, the portion of thereference frame searched, which may be referred to as the search area,may include a limited number of rows of the reference frame. In anexample, identifying the reference block may include calculating a costfunction, such as a sum of absolute differences (SAD), between thepixels of the blocks in the search area and the pixels of the currentblock. In some implementations, more than one reference frame may beprovided. For example, three reference frames may be selected from eightcandidate reference frames.

In some implementations, the spatial difference between the location ofthe reference block in the reference frame and the current block in thecurrent frame may be represented as a motion vector. The difference inpixel values between the reference block and the current block may bereferred to as differential data, residual data, or as a residual block.Generating motion vectors may be referred to as motion estimation, and apixel of a current block may be indicated based on location usingCartesian coordinates as f_(x,y). Similarly, a pixel of the search areaof the reference frame may be indicated based on location usingCartesian coordinates as r_(x,y). A motion vector (MV) for the currentblock may be determined based on, for example, a SAD between the pixelsof the current frame and the corresponding pixels of the referenceframe.

Although described herein with reference to matrix or Cartesianrepresentation of a frame for clarity, a frame may be stored,transmitted, processed, or any combination thereof, in any datastructure such that pixel values may be efficiently represented for aframe or image. For example, a frame may be stored, transmitted,processed, or any combination thereof, in a two dimensional datastructure such as a matrix, or in a one dimensional data structure, suchas a vector array.

For inter-prediction, the encoder 400 may convey encoded information forprediction blocks at block end points, including but not limited to aprediction mode, the prediction reference frame(s), motion vector(s) ifneeded, and subpixel interpolation filter type.

FIG. 6 is a block diagram of a representation of inter-prediction usinga subpixel interpolation filter in accordance with implementations ofthis disclosure. Inter-prediction using a subpixel interpolation filtermay be implemented in a decoder, such as the decoder 500 shown in FIG. 5, an encoder, such as the encoder 400 shown in FIG. 4 , or both.

In some implementations, inter-prediction may include encoding a currentframe 610, or a portion thereof, such as block 612 or block 614, withreference to a reference frame 620. For example, a motion vector 632/634may indicate a spatial location of a reference block 622/624 in thereference frame 620 relative to the location of the corresponding block612/614 in the current frame 610, the reference block 622/624 may be theportion of the reference frame 620 identified as most accuratelymatching the corresponding block 612/614 in the current frame 610, andthe reference block 622/624 may be used to generate a prediction blockfor encoding the current frame 610.

In some implementations, the portion 626 of the reference frame 620 thatmost accurately matches a current block 614 of the current frame 610 maybe offset from block or pixel boundaries, and inter-prediction mayinclude using a subpixel interpolation filter. For example,inter-prediction may include using motion vector precision of ½ pel, ¼pel, or ⅛ pel, and a subpixel interpolation filter may be used.

In some implementations, coding a current block may include identifyinga prediction mode from multiple candidate prediction modes for codingthe current block. For example, a video coder may evaluate the candidateprediction modes, which may include intra-prediction modes,inter-prediction modes, or both, to identify the optimal predictionmode. The optimal prediction mode may be, for example, the predictionmode that minimizes an error metric, such as a rate-distortion cost, forthe current block.

In some implementations, the inter-prediction modes may include a newmotion vector mode (NewMV), a zero motion vector mode (ZeroMV), anearest motion vector mode (NearestMV), and a near motion vector mode(NearMV). The new motion vector mode (NewMV) may indicate that a newmotion vector for the current block may be signaled expressly orexplicitly in the encoded video stream. In some implementations, the newmotion vector may be signaled differentially. For example, the newmotion vector may be signaled using a difference between the new motionvector and a reference motion vector, such as a motion vector used forencoding a previously coded neighboring block. The zero motion vectormode (ZeroMV) may indicate that a zero motion vector, (0,0), which mayindicate no motion, may be used for predicting the current block, and anexpress or explicit motion vector for predicting the current block maybe omitted from the encoded video stream. In some implementations, thenearest motion vector mode (NearestMV) may indicate that a motion vectorused for encoding a neighboring previously encoded block identified asthe nearest motion vector may be used for predicting the current block,and an express or explicit motion vector for predicting the currentblock may be omitted from the encoded video stream. In someimplementations, the near motion vector mode (NearMV) may indicate thata motion vector used for encoding a neighboring previously encoded blockidentified as the near motion vector may be used for predicting thecurrent block, and an express or explicit motion vector for predictingthe current block may be omitted from the encoded video stream.

In some implementations, the encoder may identify candidate motionvectors for encoding the current block. For example, the candidatemotion vectors may include the zero motion vector, a new motion vector,a near motion vector, and a nearest motion vector. In some embodiments,the encoder may evaluate neighboring, or proximal, previously encodedblocks to identify the near motion vector and the nearest motion vector.For example, the near motion vector may be identified from a firstneighboring, or proximal, previously encoded block, and the nearestmotion vector may be identified from a second neighboring, or proximal,previously encoded block.

In some implementations, the decoder may identify candidate motionvectors for decoding a current block. For example, the candidate motionvectors may include a near motion vector, and a nearest motion vector.In some embodiments, the decoder may evaluate neighboring, or proximal,previously decoded blocks to identify the near motion vector and thenearest motion vector. For example, the near motion vector may beidentified from a first neighboring, or proximal, previously decodedblock, and the nearest motion vector may be identified from a secondneighboring, or proximal, previously decoded block.

In some implementations, coding the current block may includeidentifying an interpolation filter for predicting the current block.For example, an interpolation filter may be selected from candidateinterpolation filters. In some implementations, the candidateinterpolation filters may be 1/16-pel precision filters, and may includea Bilinear filter, an 8-tap filter (EIGHTTAP), a sharp 8-tap filter(EIGHTTAP_SHARP), a smooth 8-tap filter (EIGHTTAP_SMOOTH), or acombination thereof.

FIG. 7 is a flowchart diagram of an example method for encoding using aninterpolation filter associated with a motion vector in accordance withimplementations of this disclosure. In some implementations, encodingusing an interpolation filter associated with a motion vector may beimplemented in an encoder, such as the encoder 400 shown in FIG. 4 .

In some implementations, encoding using an interpolation filterassociated with a motion vector may include encoding a first block at710, outputting a motion vector and interpolation filter identifier forthe first block at 720, identifying candidate motion vectors forencoding a second block at 730, identifying a prediction mode forencoding the second block at 740, outputting a prediction mode forencoding the second block at 750, or a combination thereof.

In some implementations, a first block may be encoded at 710. Forexample, an encoder, such as the encoder 400 shown in FIG. 4 , mayencode a first block of a current frame, such as the block at the topleft of the frame 610 shown in FIG. 6 . In some implementations,encoding the first block may include identifying a motion vector forencoding the first block. Although not shown separately in FIG. 7 , insome implementations, identifying the motion vector for encoding thefirst block may include identifying candidate motion vectors forencoding the first block. The candidate motion vectors may include a newmotion vector, a zero motion vector, a near motion vector, a nearestmotion vector, or a combination thereof. The near motion vector and thenearest motion vector may be identified by evaluating previously encodedblocks neighboring, or proximate to, the first block in the currentframe. For example, the blocks of the current frame may be encoded inraster scan order, and the previously encoded blocks neighboring thefirst block in the first frame may include the block to the left of thefirst block, the block above the first block, the block above and to theleft of the first block, the block above and to the right of the firstblock, or a combination thereof. In some implementations, the new motionvector may be identified for encoding the first block and aninterpolation filter may be identified for encoding the first block. Insome implementations, the interpolation filter may be a subpixelinterpolation filter such as a Bilinear filter, an 8-tap filter(EIGHTTAP), a sharp 8-tap filter (EIGHTTAP_SHARP), or a smooth 8-tapfilter (EIGHTTAP_SMOOTH).

In some implementations, a reference block may be identified in areference frame based on the motion vector, and a prediction block maybe generated from the reference block using the interpolation filter. Insome implementations, a residual, or prediction error, between theinput, or source, first block and the prediction block may be includedin the output bitstream.

In some implementations, the motion vector and an identifier of theinterpolation filter used for coding the first block may be included inthe output bitstream at 720, such as in a header for the first block. Insome implementations, the motion vector for coding the first block maybe associated with the interpolation filter for coding the first block.

In some implementations, a second, or current, block of the currentframe may be encoded subsequent to encoding the first block of thecurrent frame. For example, an encoder, such as the encoder 400 shown inFIG. 4 , may encode a second block, such as block 614 from frame 610shown in FIG. 6 .

In some implementations, encoding the current block may includeidentifying candidate motion vectors for encoding a current block at730. The candidate motion vectors may include a new motion vector, azero motion vector, a near motion vector, a nearest motion vector, or acombination thereof. The near motion vector and the nearest motionvector may be identified by evaluating previously encoded blocksneighboring, or proximate to, the current block in the current frame.For example, the blocks of the current frame may be encoded in rasterscan order, and the previously encoded blocks neighboring the currentblock in the current frame may include the block to the left of thecurrent block, the block above the current block, the block above and tothe left of the current block, the block above and to the right of thecurrent block, or a combination thereof; however different previouslyencoded blocks neighboring the current block, or a different encodingorder may be used. In some embodiments, the first block encoded at 710may be a previously encoded block neighboring the current block in thecurrent frame, and the motion vector used for encoding the first blockmay be identified as the near motion vector or the nearest motion vectorfor coding the current block.

In some implementations, a prediction mode may be identified forencoding the second block at 740. For example, an inter-prediction mode,such as new motion vector mode (NewMV), zero motion vector mode(ZeroMV), nearest motion vector mode (NearestMV), or near motion vectormode (NearMV), may be identified for encoding the current block.

In some implementations, the nearest motion vector mode may beidentified for encoding the current block, and a corresponding nearestmotion vector may be identified as the motion vector for encoding thecurrent block. For example, the first block may be a previously encodedblock neighboring the current block in the current frame, the motionvector used for encoding the first block may be identified as thenearest motion vector, the prediction mode for encoding the currentblock may be identified as the nearest motion vector mode, and themotion vector used for encoding the first block may be identified as themotion vector for encoding the current block. Similarly, in someimplementations, the near motion vector mode may be identified forencoding the current block, and a corresponding near motion vector maybe identified as the motion vector for encoding the current block. Forexample, the first block may be a previously encoded block neighboringthe current block in the current frame, the motion vector used forencoding the first block may be identified as the near motion vector,the prediction mode for encoding the current block may be identified asthe near motion vector mode, and the motion vector used for encoding thefirst block may be identified as the motion vector for encoding thecurrent block.

In some implementations, identifying the prediction mode at 740 mayinclude identifying an interpolation filter for encoding the currentblock based on the motion vector identified for encoding the currentblock. In some implementations, the motion vector identified forencoding the current block may be a new motion vector, and identifyingthe interpolation filter for encoding the current block may includeevaluating candidate interpolation filters to identify an optimalinterpolation filter. In some implementations, the motion vectoridentified for encoding the current block may be the nearest motionvector and the interpolation filter used for encoding the blockcorresponding to the nearest motion vector may be identified as theinterpolation filter for encoding the current block. For example, themotion vector used for encoding the first block may be identified as thenearest motion vector, the prediction mode may be identified as nearestmotion vector mode, and the interpolation filter used for encoding thefirst block may be identified as the interpolation filter for encodingthe second block. In some implementations, the motion vector identifiedfor encoding the current block may be the near motion vector and theinterpolation filter used for encoding the block corresponding to thenear motion vector may be identified as the interpolation filter forencoding the current block. For example, the motion vector used forencoding the first block may be identified as the near motion vector,the prediction mode may be identified as the near motion vector mode,and the interpolation filter used for encoding the first block may beidentified as the interpolation filter for encoding the second block.

In some implementations, for encoding the current frame, a referenceblock may be identified in a reference frame based on the identifiedmotion vector, and a prediction block may be generated from thereference block using the identified interpolation filter. In someimplementations, a residual, or prediction error, between the input, orsource, current block and the prediction block may be included in theoutput bitstream.

In some implementations, the prediction mode used for coding the currentblock may be included in the output bitstream at 750, such as in aheader for the current block. In some implementations, the motion vectorand an identifier of the interpolation filter used for coding thecurrent block may be omitted from the output bitstream. For example, theprediction mode may be identified as the nearest motion vector mode, thenear motion vector mode, or the zero motion vector mode, the predictionmode may be included in the output bitstream, and the motion vector andan identifier of the interpolation filter may be omitted from the outputbitstream.

FIG. 8 is a flowchart diagram of an example of a method for decodingusing an interpolation filter associated with a motion vector inaccordance with implementations of this disclosure. In someimplementations, decoding using an interpolation filter associated witha motion vector may be implemented in a decoder, such as the decoder 500shown in FIG. 5 .

In some implementations, decoding using an interpolation filterassociated with a motion vector may include decoding first block at 810,decoding a prediction mode for decoding a second, or current, block at820, identifying a motion vector and an associated interpolation filterfor decoding the current block at 830, or a combination thereof.

In some implementations, first block of a current frame may be decodedat 810. In some implementations, decoding the first block may includedecoding a prediction mode, such as new motion vector mode, for decodingthe first block. In some implementations, the prediction mode may be thenew motion vector mode and decoding the first block may include decodinga motion vector and an identifier of an interpolation filter, such as asubpixel interpolation filter for decoding the first block. In someimplementations, decoding the first block may include decoding aresidual, or prediction error for the first block. In someimplementations, decoding the first block may include identifying areference block in a reference frame based on the decoded motion vector,generating a predicted block from the reference block using theinterpolation filter indicated by the decoded interpolation filteridentifier, and generating a reconstructed block by adding the decodedresidual to the predicted block. In some implementations, the predictionmode, the motion vector, the identifier of the interpolation filter, ora combination thereof, may be decoded from a header for the first blockin the encoded video stream. In some implementations, the reconstructedblock may be included in an output, such as an output for presentation.

In some implementations, a prediction mode for decoding a second, orcurrent, block may be identified at 820. In some implementations,identifying the prediction mode for decoding the second block mayinclude decoding the prediction mode from the encoded bitstream. Forexample, the prediction mode may be decoded from a header for thecurrent block in the encoded video steam. In some implementations, theheader for the current block may omit a motion vector, an identifier ofan interpolation filter, or both, for decoding the current block. Insome implementations, the decoded prediction mode may indicate thenearest motion vector mode, the near motion vector mode, or the zeromotion vector mode, and the encoded video stream may omit a motionvector and an identifier of an interpolation filter for decoding thecurrent block.

In some implementations, a motion vector and an associated interpolationfilter for decoding the current block may be identified at 830. Forexample, the prediction mode for decoding the current block identifiedat 820 may be the nearest motion vector mode or the near motion vectormode, and a motion vector and an associated interpolation filter fordecoding the current block may be identified.

In some implementations, identifying the motion vector for decoding thecurrent block may include identifying candidate motion vectors fordecoding the current block. Identifying the candidate motion vectors mayinclude identifying a near motion vector, a nearest motion vector, orboth. The near motion vector and the nearest motion vector may beidentified by evaluating previously decoded blocks neighboring, orproximate to, the current block in the current frame. For example, theblocks of the current frame may be decoded in raster scan order, and thepreviously decoded blocks neighboring the current block in the currentframe may include the block to the left of the current block, the blockabove the current block, the block above and to the left of the currentblock, the block above and to the right of the current block, or acombination thereof; however different previously decoded blocksneighboring the current block, or a different decoding order may beused. In some embodiments, the first block decoded at 810 may be apreviously decoded block neighboring the current block in the currentframe, and the motion vector used for decoding the first block may beidentified as the near motion vector or the nearest motion vector fordecoding the current block. In some embodiments where the previouslydecoded blocks spatially proximal to the current block (e.g., a secondblock) include the first block, the selected previously decoded blockfrom which the motion vector for the first block is identified isomitted from the previously decoded blocks spatially proximal to thecurrent block.

In some embodiments, the prediction mode decoded for the second block at820 may be the nearest motion vector mode, the first block decoded at810 may be a previously decoded block neighboring the current block inthe current frame, and the motion vector used for decoding the firstblock may be identified as the nearest motion vector for decoding thecurrent block, and, based on the decoded prediction mode for the currentblock, the motion vector used for decoding the first block may beidentified as the selected motion vector for decoding the current block.Similarly, the prediction mode decoded for the second block at 820 maybe the near motion vector mode, the first block decoded at 810 may be apreviously decoded block neighboring the current block in the currentframe, and the motion vector used for decoding the first block may beidentified as the near motion vector for decoding the current block,and, based on the decoded prediction mode for the current block, themotion vector used for decoding the first block may be identified as theselected motion vector for decoding the current block.

In some implementations, an interpolation filter associated with theselected motion vector may be identified as the interpolation filter forencoding the current block.

For example, the prediction mode decoded for the second block at 820 maybe the nearest motion vector mode, the first block decoded at 810 may bea previously decoded block neighboring the current block in the currentframe, and the motion vector used for decoding the first block may beidentified as the nearest motion vector for decoding the current block,based on the decoded prediction mode for the current block, the motionvector used for decoding the first block may be identified as theselected motion vector for decoding the current block, and, based on theselected motion vector the interpolation filter used for decoding thefirst block, which may be associated with the selected motion vector,may be identified as the selected interpolation filter for decoding thecurrent block. Similarly, the prediction mode decoded for the secondblock at 820 may be the near motion vector mode, the first block decodedat 810 may be a previously decoded block neighboring the current blockin the current frame, the motion vector used for decoding the firstblock may be identified as the near motion vector for decoding thecurrent block, based on the decoded prediction mode for the currentblock, the motion vector used for decoding the first block may beidentified as the selected motion vector for decoding the current block,and, based on the selected motion vector the interpolation filter usedfor decoding the first block, which may be associated with the selectedmotion vector, may be identified as the selected interpolation filterfor decoding the current block.

In some implementations, decoding the current block may includeidentifying a reference block in a reference frame based on the selectedmotion vector, generating a predicted block from the reference blockusing the selected interpolation filter, and generating a reconstructedblock by adding the decoded residual to the predicted block. In someimplementations, the reconstructed block may be included in an output,such as an output for presentation.

The words “example” or “exemplary” are used herein to mean serving as anexample, instance, or illustration. Any aspect or design describedherein as “example” or “exemplary” not necessarily to be construed aspreferred or advantageous over other aspects or designs. Rather, use ofthe words “example” or “exemplary” is intended to present concepts in aconcrete fashion. As used in this application, the term “or” is intendedto mean an inclusive “or” rather than an exclusive “or”. That is, unlessspecified otherwise, or clear from context, “X includes A or B” isintended to mean any of the natural inclusive permutations. That is, ifX includes A; X includes B; or X includes both A and B, then “X includesA or B” is satisfied under any of the foregoing instances. In addition,the articles “a” and “an” as used in this application and the appendedclaims should generally be construed to mean “one or more” unlessspecified otherwise or clear from context to be directed to a singularform. Moreover, use of the term “an embodiment” or “one embodiment” or“an implementation” or “one implementation” throughout is not intendedto mean the same embodiment or implementation unless described as such.As used herein, the terms “determine” and “identify”, or any variationsthereof, includes selecting, ascertaining, computing, looking up,receiving, determining, establishing, obtaining, or otherwiseidentifying or determining in any manner whatsoever using one or more ofthe devices shown in FIG. 1 .

Further, for simplicity of explanation, although the figures anddescriptions herein may include sequences or series of steps or stages,elements of the methods disclosed herein can occur in various ordersand/or concurrently. Additionally, elements of the methods disclosedherein may occur with other elements not explicitly presented anddescribed herein. Furthermore, not all elements of the methods describedherein may be required to implement a method in accordance with thedisclosed subject matter.

The implementations of the transmitting station 100A and/or thereceiving station 100B (and the algorithms, methods, instructions, etc.stored thereon and/or executed thereby) can be realized in hardware,software, or any combination thereof. The hardware can include, forexample, computers, intellectual property (IP) cores,application-specific integrated circuits (ASICs), programmable logicarrays, optical processors, programmable logic controllers, microcode,microcontrollers, servers, microprocessors, digital signal processors orany other suitable circuit. In the claims, the term “processor” shouldbe understood as encompassing any of the foregoing hardware, eithersingly or in combination. The terms “signal” and “data” are usedinterchangeably. Further, portions of the transmitting station 100A andthe receiving station 100B do not necessarily have to be implemented inthe same manner.

Further, in one implementation, for example, the transmitting station100A or the receiving station 100B can be implemented using a computerprogram that, when executed, carries out any of the respective methods,algorithms and/or instructions described herein. In addition oralternatively, for example, a special purpose computer/processor can beutilized that contains specialized hardware for carrying out any of themethods, algorithms, or instructions described herein.

The transmitting station 100A and the receiving station 100B can, forexample, be implemented on computers in a real-time video system.Alternatively, the transmitting station 100A can be implemented on aserver and the receiving station 100B can be implemented on a deviceseparate from the server, such as a hand-held communications device. Inthis instance, the transmitting station 100A can encode content using anencoder 400 into an encoded video signal and transmit the encoded videosignal to the communications device. In turn, the communications devicecan then decode the encoded video signal using a decoder 500.Alternatively, the communications device can decode content storedlocally on the communications device, for example, content that was nottransmitted by the transmitting station 100A. Other suitableimplementation schemes for the transmitting station 100A and thereceiving station 100B implementation schemes are available. Forexample, the receiving station 100B can be a generally stationarypersonal computer rather than a portable communications device and/or adevice including an encoder 400 may also include a decoder 500.

Further, all or a portion of implementations can take the form of acomputer program product accessible from, for example, a tangiblecomputer-usable or computer-readable medium. A computer-usable orcomputer-readable medium can be any device that can, for example,tangibly contain, store, communicate, or transport the program for useby or in connection with any processor. The medium can be, for example,an electronic, magnetic, optical, electromagnetic, or a semiconductordevice. Other suitable mediums are also available.

The above-described implementations have been described in order toallow easy understanding of the application are not limiting. On thecontrary, the application covers various modifications and equivalentarrangements included within the scope of the appended claims, whichscope is to be accorded the broadest interpretation so as to encompassall such modifications and equivalent structure as is permitted underthe law.

What is claimed is:
 1. A method, comprising: decoding a first block of acurrent frame from an encoded video stream, wherein decoding the firstblockcm includes: decoding a first motion vector from the encoded videostream; decoding, from the encoded video stream, an identifier of afirst interpolation filter for subpixel interpolation; andreconstructing the first block using the first motion vector and thefirst interpolation filter; decoding, by a processor, using a selectedmotion vector and a selected interpolation filter, a second block of thecurrent frame from the encoded video stream, wherein decoding the secondblock includes: decoding an inter-prediction mode; in response to theinter-prediction mode indicating that the first motion vector of thefirst block is to be used for reconstructing the second block:identifying the first motion vector from the first block as the selectedmotion vector for predicting the second block; omitting decoding, fromthe encoded video stream, the selected interpolation filter; andidentifying the first interpolation filter that is associated with thefirst motion vector as the selected interpolation filter for predictingthe second block; in response to the inter-prediction mode indicating anew motion vector mode: decoding, from the encoded video stream, theselected motion vector; decoding, from the encoded video stream, theidentifier of the selected interpolation filter; and reconstructing thesecond block using the selected motion vector and the selectedinterpolation filter; decoding a third block of the current frame fromthe encoded video stream, wherein decoding the third block includes:identifying previously decoded blocks spatially proximal to the thirdblock in the current frame, wherein the previously decoded blocksinclude the second block and omit the first block; identifying thesecond block from the previously decoded blocks in response to decodingthe interprediction mode for decoding the third block; identifying thefirst motion vector from the first block as a selected motion vector forpredicting the third block in response to identifying the second blockfrom the previously decoded blocks; identifying the first interpolationfilter as a selected interpolation filter for predicting the third blockin response to identifying the first motion vector from the first blockas the selected motion vector for predicting the third block; andreconstructing the third block using the first motion vector and thefirst interpolation filter; and outputting or storing the first block,the second block, and the third block.
 2. The method of claim 1, whereinthe first motion vector is a non-zero motion vector.
 3. The method ofclaim 1, wherein decoding the first block includes: identifyinginformation associating the first interpolation filter with the firstmotion vector.
 4. The method of claim 3, wherein identifying the firstinterpolation filter as the selected interpolation filter for predictingthe second block includes identifying the first interpolation filterbased on the information associating the first interpolation filter withthe first motion vector.
 5. The method of claim 1, wherein decoding thesecond block is subsequent to decoding the first block.
 6. The method ofclaim 5, wherein the first block is spatially proximal to the secondblock in the current frame.
 7. A method comprising: decoding, by aprocessor in response to instructions stored on a non-transitorycomputer readable medium, using a selected motion vector and a selectedinterpolation filter, a current block of a current frame from an encodedvideo stream, wherein decoding the current block includes: decoding,from the encoded video stream, an inter-prediction mode; in response tothe inter-prediction mode indicating that the selected motion vector isa motion vector of one of previously decoded blocks: identifying the amotion vector from a first selected previously decoded block of thepreviously decoded blocks as the a first selected motion vector forpredicting the a current block; omitting decoding, from the encodedvideo stream, the selected interpolation filter; and identifying aninterpolation filter that is associated with the first selected motionvector from the first selected previously decoded block as the a firstselected interpolation filter for predicting the current block; andreconstructing the current block using the first selected motion vectorand the first selected interpolation filter; decoding a second block ofthe current frame from the an encoded video stream, wherein decoding thesecond block includes: identifying previously decoded blocks spatiallyproximal to the second block in the current frame, wherein thepreviously decoded blocks spatially proximal to the second block includethe current block and omit the first selected previously decoded blockfrom the previously decoded blocks spatially proximal to the currentblock; identifying the current block from the previously decoded blocksspatially proximal to the second block in response to decoding the aninter-prediction mode for decoding the second block as the a secondselected previously decoded block for predicting the second block;identifying, as a second selected motion vector for predicting thesecond block, the motion vector from the second selected previouslydecoded block from the previously decoded blocks spatially proximal tothe current block in response to identifying the current block from thepreviously decoded blocks as the second selected previously decodedblock for predicting the second block; identifying the interpolationfilter, as a second selected interpolation filter for predicting thesecond block, in response to identifying the motion vector as the secondselected motion vector for predicting the second block; andreconstructing the second block using the second selected motion vectorfor predicting the second block and the second selected interpolationfilter for predicting the second block; and outputting or storing thecurrent block and the second block.
 8. The method of claim 7, whereindecoding the current block includes further comprising: decoding aheader for the current block from the encoded video stream, wherein theheader includes the inter-prediction mode for decoding the currentblock, and wherein the header omits an identifier of a selected theinterpolation filter for predicting the current block and omits aselected the motion vector for predicting the current block.
 9. Themethod of claim 7, wherein the motion vector is a non-zero motionvector.
 10. A method, comprising: generating a first encoded block byencoding a first block from a current frame from an input video stream,wherein encoding the first block includes: identifying a first motionvector for predicting the first block, wherein the first motion vectorhas sub-pixel precision; and identifying a first interpolation filterfor predicting the first block; outputting the first encoded block by:including, in an output bitstream, a first inter-prediction modeindicative of the first motion vector; and including, in the outputbitstream, a first identifier of the first interpolation filter;generating, by a processor, a second encoded block by encoding a secondblock from the current frame, wherein encoding the second blockincludes: identifying candidate motion vectors for predicting the secondblock, wherein the candidate motion vectors include the first motionvector; identifying, from the candidate motion vectors, a selectedmotion vector for predicting the second block; in response todetermining that the selected motion vector for predicting the secondblock is the first motion vector used for predicting the first block:identifying the first interpolation filter as a selected interpolationfilter for predicting the second block; predicting the second blockusing the first motion vector and the first interpolation filter; andomitting encoding, in the output bitstream, the selected motion vectorfor predicting the second block and an identifier of the selectedinterpolation filter for predicting the second block; generating a thirdencoded block by encoding a third block from the current frame, whereinencoding the third block includes: identifying previously coded blocksproximal to the third block in the current frame, wherein the previouslycoded blocks proximal to the third block include the second block andomit the first block; identifying candidate motion vectors forpredicting the third block based on the previously coded blocks, whereinthe candidate motion vectors include the first motion vector;identifying, from the candidate motion vectors for predicting the thirdblock, a selected motion vector for predicting the third block; on acondition that the selected motion vector for predicting the third blockis the first motion vector: identifying the first interpolation filteras a selected interpolation filter for predicting the third block; andomitting the selected motion vector for predicting the third block andan identifier of the selected interpolation filter for predicting thethird block from the output bitstream; and transmitting or storing theoutput bitstream.
 11. The method of claim 10, wherein the first motionvector is a non-zero motion vector.
 12. The method of claim 10, whereinincluding the first identifier of the first interpolation filter in theoutput bitstream includes including the first identifier of the firstinterpolation filter in the output bitstream such that the first motionvector is associated with the first interpolation filter.
 13. The methodof claim 10, wherein encoding the second block is subsequent to encodingthe first block.
 14. The method of claim 10, wherein the selected motionvector is a new motion vector, the method further comprising: on acondition that the selected motion vector being a new motion vector:evaluating candidate interpolation filters to identify a secondinterpolation filter for encoding the second block; and encoding asecond identifier indicative of the second interpolation filterassociated with the selected motion vector.